One of the key themes that has come out from the revelations concerning NSA surveillance is a bunch of defenders of the program claiming "it's just metadata." This is wrong on multiple levels. First of all, only some of the revealed programs involve "just metadata." The so-called "business records" data is metadata, but other programs, such as PRISM, can also include actual content. But, even if we were just talking about "just metadata," the idea that it somehow is no big deal, and people have nothing to worry about when it comes to metadata is ridiculous to anyone who knows even the slightest thing about metadata. In fact, anyone who claims that "it's just metadata" in an attempt to minimize what's happening is basically revealing that they haven't the slightest clue about what metadata is. Here are a few examples of why.

Just a few months ago, Nature published a study all about how much a little metadata can reveal, entitled Unique in the Crowd: The privacy bounds of human mobility by Yves-Alexandre de Montjoye, Cesar A. Hidalgo, Michel Verleysen, and Vincent D. Blondel. The basic conclusion: metadata reveals a ton, and even "coarse datasets" provide almost no anonymity...